This invention relates to a test medium and method for detecting phosphorus segregates, and more particularly, to such a medium and method capable of rapidly and easily detecting the distribution of phosphorus in metallic materials such as continuously cast steel slabs and large-sized steel ingots by utilizing electrolysis.
It is well known in the art that continuously cast steel slabs and large-sized steel ingots have such elements as sulfur (S), phosphorus (P), manganese (Mn), silicon (Si), and carbon (C) locally concentrated or segregated in their central area, and these segregated elements have a great influence on the quality of steel products. In the prior art, such central segregation was judged by sulfur printing in iron-making works. This method is by attaching photographic paper impregnated with aqueous sulfuric acid to a polished cross section of a large-sized steel ingot, thereby detecting hydrogen sulfide given off from segregated sulfur as stains on the photographic paper. The distribution of sulfur is two-dimensionally developed on a photographic paper sheet.
As a new segregate detecting method substituting for the sulfur printing method, we developed a phosphorus printing method, that is, a method for detecting phosphorus segregates by selectively etching a phosphorus segregated area with a copper or silver nitrate solution, transferring phosphorus or iron to test paper, and subjecting the occluded phosphorus or iron to color development as disclosed in Japanese Patent Application Nos. 58-213497, 59-153799, 59-170227, 59-174828, and 59-180016.
One old method of detecting phosphorus is the phosphorus printing reported by M. Niessner in 1932. This method is by attaching filter paper which has been impregnated with liquid II shown below in Table 1 to a surface area of steel to be examined for 3 to 5 minutes, removing the paper from the steel surface, and thereafter dipping the filter paper in liquid I for 3 to 5 minutes, thereby producing a printed image.
TABLE 1 ______________________________________ Liquid I Saturated stannous chloride solution 5 ml Conc. hydrochloric acid 50 ml Water 100 ml Alum minor amount Liquid II Ammonium molybdate 5 grams Water 100 ml Nitric acid (specific gravity 1.2) 35 ml ______________________________________
Since specimen surface is maintained in contact with 1.8N nitric acid, the matrix is severely attacked and phosphorus is dissolved out there. When the removed test paper is dipped in liquid I, it turns blue over the entire surface. This method is only useful to estimate the amount of phosphorus in the matrix, but difficult to detect phosphorus segregates in commercial grade steels (see FIG. 6).
When it is desired to detect segregates in solidified stainless steel, the afore-mentioned sulfur and phosphorus printing methods are useless because any etching solutions used therein can attack or dissolve a surface area to be examined to an insufficient extent to detect segregates. There is a strong need for a phosphorus segregate detecting medium and method which are also applicable to stainless steel.